The present invention relates to semiconductor device packages, and in particular, to lead frame apparatus and method for improved wire bonding in manufacturing of a semiconductor device.
In semiconductor device packaging, the semiconductor chip is electrically connected to outside circuitry by a lead frame. An example lead frame may be a solid metal frame with fingers radiating inward from opposing sides. At a center of the fingers may be a die attach pad or paddle where a semiconductor die may be attached.
The electrical connections of the semiconductor die may be made by wire bonding from pads located on top of the semiconductor die to finger ends of the metal lead frame. The semiconductor die and a portion of the lead frame fingers are then encapsulated or molded in a material such as an epoxy or plastic molding compound, and the molded package body and lead frame fingers are cut from the frame. The lead frame fingers are then formed to provide a means of electrically connecting the package to a printed circuit board. The severed fingers therefore constitute the I/O (Input/Output) leads for the semiconductor device (a.k.a. a micro chip).
FIG. 1A illustrates a semiconductor device 100 which utilizes a typical lead frame. Semiconductor device 100 shows a dashed line indicating a die attach pad 101 within the mold compound, a dashed line indicating a semiconductor die 102 within the mold compound, and a dashed line indicating a portion 103 of the semiconductor device 100. FIG. 1B illustrates the portion 103 of the semiconductor device 100 of FIG. 1A in a cut-away view. Die 102 is attached to die attach pad 101.
The typical lead frame shown in FIG. 1B has long bond wire lengths (e.g. distance 120) and small distances between bond pads (e.g. distance 116) which may cause electrical shorts during manufacturing. During the molding process, wire bonds may be moved (i.e. wire sweep) during the flowing and curing of the mold compound. Adjacent bond wires with short lengths and ample spacing between the bond wires may not move much and therefore are less likely to short together. However, adjacent bond wires that are longer (e.g. bond wires 106 and 107) or with less spacing between them (e.g. bond wires 104 and 105) may be more likely to electrically short together during the molding process.
The typical lead frame has a problem with the length of the bond wires which attach to the corner regions of the lead frame. For example, bond wires 106-107 attach corner lead frame fingers 114-115 to bond pads 110-111, respectively. Distance 120 is longer than a distance traversed by bond wire 104 or 105. Fingers 114-115 extend out in the x direction away from the corner of die 102 due to the minimum width available in manufacturing a lead frame finger.
Another problem with the typical lead frame concerns the distance between bond wires. This may be especially problematic when the density of bond pads is disproportionately arranged on a semiconductor die. For example, example die 102 has more bond pads per unit area on side A as compared to side B. In this case, the bond pads on side A (e.g. bond pads 108-111) may require bond wires which attach to fingers which are not on the same side of the lead frame. For example, fingers 112-115 are utilized to attach to bond pads 108-111 located along side A. An angle of approach 119 results in a distance 117 between bond wires 106 and 107. An angle of approach 118 results in a distance 116 between bond wires 104 and 105.
Thus, it would be desirable to provide lead frames with improved wire bonding.